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Articles by Asad Jan
Total Records ( 3 ) for Asad Jan
  Asad Jan , Qazi M. Hassan , Tahira Fatima and Tayyab Hasnain
  Four rice genotypes i.e. Swat I, Swat II, Dilrosh 97 and Pakhal were tested for their callus induction frequency and their subsequent regeneration from different explants on a variety of media combinations. Swat I appeared to be the most responsive genotype to callus induction followed by Swat II, Dilrosh 97 and Pakhal respectively. Swat I and Swat II produced high amount of callus compared to other genotypes. Callus induction frequencies ranged from 68.88 to 57.70 percent in Swat I, 60.00 percent in Swat II, 52.20 percent in Dilrosh 97 and 40.00 to 42.20 percent in Pakhal from scutella on two different media. Similar response was also found for root induced calli. However, N6 medium containing 2 mg/l of 2,4-D was found to be optimum for callus induction irrespective of the genotypes and explant studied. All varieties showed significant differences in regeneration from two and three week old calli. RM medium containing MS salts and vitamins, 2 gm casamino acid, 1 mg/l NAA, 2 mg/l BAP and 30 gm sorbitol gave comparatively higher regeneration response than the other two media tested. Plants regenerated were grown in harmone free MS medium for vigorous rooting and subsequent transfer to soil.
  Tahira Fatima , Asad Jan , Tayyab Husnain and Sheikh Riazuddin
  Efforts were made to optimize tissue culture conditions for quick establishment of cell suspension and simple procedure for the cryopreservation of embryogenic cells suspension cultures of three rice varieties. Suspension cultures were initiated from friable, globular embryogenic calli in MS/R2 media supplemented with 2mg/l 2,4-D. These suspension cultures were regenerated and cryopreserved. Both MS and R2 media supplemented with 2mg/l 2,4-D were quiet suitable for developing cell suspension. All the three varieties gave compact light yellow calli on MMS medium. The regeneration frequency was 55% on average for 10-14 weeks old cell suspension. Vigorous regeneration was observed on MS containing sorbitol. Post thaw cell viability varied from variety to variety. No significant difference in viability was found in varieties cryopreserved for different periods. In conclusion cryopreservation can be used to preserve cell suspension line for a reasonable time. It can easily be used on culture medium or liquid R2 medium.
  Asad Jan , Ozgun Gokce , Ruth Luthi-Carter and Hilal A. Lashuel
  Aggregation and fibril formation of amyloid-β (Aβ) peptides Aβ40 and Aβ42 are central events in the pathogenesis of Alzheimer disease. Previous studies have established the ratio of Aβ40 to Aβ42 as an important factor in determining the fibrillogenesis, toxicity, and pathological distribution of Aβ. To better understand the molecular basis underlying the pathologic consequences associated with alterations in the ratio of Aβ40 to Aβ42, we probed the concentration- and ratio-dependent interactions between well defined states of the two peptides at different stages of aggregation along the amyloid formation pathway. We report that monomeric Aβ40 alters the kinetic stability, solubility, and morphological properties of Aβ42 aggregates and prevents their conversion into mature fibrils. Aβ40, at approximately equimolar ratios (Aβ40/Aβ42 ~ 0.5–1), inhibits (>50%) fibril formation by monomeric Aβ42, whereas inhibition of protofibrillar Aβ42 fibrillogenesis is achieved at lower, substoichiometric ratios (Aβ40/Aβ42 ~ 0.1). The inhibitory effect of Aβ40 on Aβ42 fibrillogenesis is reversed by the introduction of excess Aβ42 monomer. Additionally, monomeric Aβ42 and Aβ40 are constantly recycled and compete for binding to the ends of protofibrillar and fibrillar Aβ aggregates. Whereas the fibrillogenesis of both monomeric species can be seeded by fibrils composed of either peptide, Aβ42 protofibrils selectively seed the fibrillogenesis of monomeric Aβ42 but not monomeric Aβ40. Finally, we also show that the amyloidogenic propensities of different individual and mixed Aβ species correlates with their relative neuronal toxicities. These findings, which highlight specific points in the amyloid peptide equilibrium that are highly sensitive to the ratio of Aβ40 to Aβ42, carry important implications for the pathogenesis and current therapeutic strategies of Alzheimer disease.
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